31-07-2012, 03:16 PM
SINGLE PHASE POWER FACTOR CORRECTION CIRCUIT WITH WIDE OUTPUT VOLTAGE RANGE
A POWER FACTOR.pdf (Size: 722.42 KB / Downloads: 181)
INTRODUCTION
With the increasing demand for power from the ac line and more stringent limits for
power quality, power factor correction has gained great attention in recent years. A
variety of circuit topologies and control methods have been developed for the PFC
application [1-22]. While the discontinuous conduction mode (DCM) converters such as
boost and flyback converters are well suited for low power applications, continuous
conduction mode (CCM) boost converters with average current mode, peak current mode
or hysteresis control are commonly chosen for many medium and high power
applications. The output voltage of the boost PFC converter should be always higher than
the peak line voltage. For universal line application (85 V-265 V), the output voltage is
ususally set around 400 VDC. Recently, a Buck+Boost PFC converter has been adopted
for wide input voltage range application [21]. The output voltage of the Buck+Boost
converter can be lower than the peak line voltage.
Buck+Boost PFC Circuit
In this section, Buck+Boost PFC converter is analyzed in terms of loss analysis and
component selection. It will be shown that this converter has several advantages and
disadvantages for the variable output voltage application. These advantages and
limitations have been carefully assessed and summarized.
Principle Operation
Boost converter is a conventional PFC circuit since its input current can be programmed
to follow the input voltage. It has several advantages, such as a small EMI filter due to its
continuous input current, and a simple circuit. The basic requirement is that the output
voltage must be higher than the input voltage. For a wide range output voltage, as in this
application, the converter outputs lower voltage, below the input voltage, when the
system operates at low power level. A Boost converter can’t accomplish this function. In
order to achieve high power factor for this operation condition, a Buck converter or the
converter which has Buck function has to be used. Fig. 2.1 shows the proposed
Buck+Boost converter. Actually, this converter combines a buck converter with a boost
converter. The basic operation can be described as follows.
Conclusions
This topology is very attractive for this typical application since boost operation mode
runs at high power while buck operation mode operates at low power (P < 1.3 kW) from
its load characteristics. From the loss analysis, this topology has a high efficiency from
light load to heavy load. In addition, a low voltage rating power device can be used.
However, this topology suffers from a disadvantage, that is, a larger EMI filter is needed
due to its discontinuous input current in the buck mode. In Section 4, a comparison
between Buck+Boost topology and Sepic converter will be given to show that this
topology has better performance.